IIRC, you'd want to make a couple changes to ride the Holdsworth. First, get a shorter (and perhaps taller) stem, and second, switch to either bar-ends or brifters. All together that's probably $200-$500 for decent parts, which would be a nice down payment on a new bike.

If you tell a bike shop employee you want to ride with your wife on local paths, they'll steer you to a hybrid. If you tell them your riding is a 50/50 mix of country road rides and riding with her, they may try to sell you two bikes, one for each.

You might be able to find something in a touring, 'cross, gravel, or "all-roads" bike that would give you:
- More relaxed / erect riding position (than flat back)
- Drop bars
- Shifters you can reach easily
- Lighter weight than the MTB
- Lower rolling resistance than the MTB

Beware, young kids in a bike shop always seem to chop the fork down as far as possible as soon as possible. You're likely going to want an uncut stem (at least to start with) with spacers so you can adjust the bar height as you get back into riding.

A good LBS would listen to you and offer you a chance to ride several from these closely related categories. Choose the one that feels best, buy it, and ride it lots!